1. Field of the Invention
This invention relates to new and improved refrigeration systems and more particularly to a system having a precooler heat exchanger for sub-cooling the refrigerant hot gas before entering the condenser.
2. Description of the Prior Art
It is well known in the art of refrigeration to improve efficiency by pre-cooling the liquid refrigerant flowing from the condenser to the receiver or flowing directly to the evaporator. Heat exchangers are employed in refrigeration systems for the exchange of heat between fluids, generally the cold refrigerant gases from the evaporator and warm liquid refrigerant from the condenser. The refrigerant gas which is exhausted from the evaporator of the refrigeration system is cold. The liquid refrigerant which s drawn from the condenser of a refrigeration system is warm. To improve the efficiency of the refrigeration system, it is desirable to heat exchange the warm liquid with the cold gas. The following patents illustrate the state of the art in pre-cooler technology:
Donovan U.S. Pat. No. 2,797,554 discloses a refrigeration apparatus including a heat exchanger which comprises, a shell construction with a central chamber and a pair of headers separated therefrom by a partition. Tube assemblies rigidly mounted on the partition and opening into the headers provide a passageway between the headers. Each tube assembly has its central portion contracting the other tube assemblies to form the walls of fluid passageways extending longitudinally along the outer surfaces thereof. Each tube assembly has ends of reduced cross-section providing a surrounding header zone in the shell at each end. Each tube assembly includes internal fins for heat exchange between fluids passing through the tube assemblies and through the central chamber shell externally of the tube assemblies. Gas is delivered to one of the headers and withdrawn from the other of the headers, and liquid is delivered to one of the header zones and withdrawn from the other header zone.
Boling, U.S. Pat. No. 2,956,419 discloses an arrangement for maintaining stable operation of refrigeration systems having air-cooled condenses throughout wide variations in the temperature of the cooling air. The invention also provides for maintaining stable operation of refrigeration systems having other types of condensers used with cooling towers.
Marlo U.S. Pat. No. 3,082,610 discloses that refrigerant flow controls are more efficient when the fluctuation of the pressures at their inlet and outlet ports are not unduly great; and that controlling the pressures at the inlet ports keeps those pressures from falling too low. In compressionexpansion refrigeration systems, the liquid pressures in the receivers of those systems should be kept from falling to unduly low levels. With water-cooled condensers, it is easy to keep the liquid pressures from falling too low; but not with air-cooled condensers. A method and apparatus are disclosed for maintaining the liquid pressure in the receiver of an air-cooled refrigeration system above a predetermined minimum level.
Bottom U.S. Pat. No. 3,446,032 discloses a liquid-liquid heat exchanger comprising an outer casing and an inner, thermally-conductive casing, each having an inlet and an outlet for fluid. The inner casing may be fluted in the direction of fluid flow to increase the heat transfer surface and to assist in maintaining turbulent flow of refrigerant. A helical coil may be provided on the inner casing. A helically spiraled strip member may be provided within the inner casing.
Hess U.S. Pat. No. 3,851,494 discloses that excessive warming of the compressor input by the heat exchanger that supercools the condenser output may be prevented by a bypass switched in and out by a thermostatic control at the output of the compressor to prevent the final compression temperature from rising to damage lubricating materials and flexible hose materials. A branching valve or a second expansion valve may be used according to whether the bypass is just around the heat exchanger or around both the heat exchanger and the evaporator.
Johnston U.S. Pat. No. 3,952,533 discloses an energy saving refrigeration system with two-phase, liquid-gas mixtures of refrigerant inlet flow having an expansion valve and a pressure regulator upstream therefrom adjusted to maintain a fixed discharge pressure to the expansion valve and having its discharge pressure set sufficiently above the evaporator boiling pressure and sufficiently below the minimum inlet pressure to the pressure regulator.
Wright U.S. Pat. No. 4,359,879 discloses a refrigeration system for cooling and drying hot, moist, compressed air.The liquid refrigerant from the condenser is sub-cooled to eliminate all flash gas and render the entire evaporator effective for refrigeration purposes. The heat exchangers for the evaporator and for sub-cooling the liquid refrigerant comprise a one-piece finned copper inner cylinder with the routed fin enclosed inside an annular copper shell in which a 0.020-inch clearance exists between the annular copper shell and the fins to allow passage of a stream of air which causes the laminar flow around the routed fin construction to be agitated by eddy diffusion. The use of the novel heat exchanger in the refrigeration system along with the step of sub-cooling the liquid refrigerant is reported to produce a substantial gain in refrigeration without an increased requirement for either power or energy.
Nunn et al U.S. Pat. No. 4,577,468 discloses the use of a sub-cooler for liquid refrigerant flowing from the condenser comprising a heat exchanger having an inner and an outer tube. The hot liquid refrigerant flows through the outer tube and a small amount of liquid refrigerant is evaporated in the inner tube to cool the liquid refrigerant.